The present invention relates to an optical diaphragm device in which an optical filter such as an infrared cutoff filter or the like is installed insertably into and retractably from a light path, and in particular, relates to a diaphragm device to be assembled to a photographic device such as a CCTV (monitor camera system) lens or the like.
A day and night monitor camera system which by day takes color photographs by focusing light in visible light region and at night takes monochrome photographs by focusing light in near-infrared light region in addition to that in the visible light region on an image picking device (CCD, CMOS or the like) of a camera body so that an monitored image is projected on a TV monitor has been known (for instance, refer to Patent Document 1).
In the daytime, this system photographs in color using light in the visible light region alone by placing an infrared cutoff filter in front of an image pickup device (inside a camera body or a lens tube), and photographs in monochrome using light in both the infrared and visible light regions by withdrawing the filter from the front of the image pickup device at night.
FIGS. 4(a) and 4(b) are views showing the structure of a conventional CCTV camera which provides an infrared cutoff filter inside its camera body.
The CCTV camera comprises a camera body 100A and a lens tube 200A fixed in front thereof An image pickup device 130 and an infrared cutoff filter 110 are provided inside the camera body 100A. In addition, a diaphragm 210 is provided inside the lens tube 200A.
The infrared cutoff filter 110 in the camera body 100A is driven by a filter driving actuator 230 provided in the camera body 100A such as a motor or the like so that the filter 110 is inserted into and retracted from a light path L in front of the image pickup device 130. FIG. 4(a) shows a state that the infrared cutoff filter 110 is inserted into the light path L, and FIG. 4(b) shows a state that the infrared cutoff filter 110 is retracted from the light path L. Meanwhile, the diaphragm 210 in the lens tube 200A is driven by a diaphragm-driving actuator 220 provided in the lens tube 200A such as a galvanometer or the like to adjust the diameter of its diaphragm aperture.
In FIG. 4(a), since the infrared cutoff filter 110 is inserted into the light path L, light incident into the lens tube 200A enters into the camera body 100A through the diaphragm 210, passes through the infrared cutoff filter 110, and reaches the image pickup device 130 to be projected as a subject image. On the other hand, in FIG. 4(b), since the infrared cutoff filter 110 is retracted from the light path L, light incident into the lens tube 200A enters into the camera body 100A via the diaphragm 210, and directly reaches the image pickup device 130 without passing through the infrared cutoff filter 110 to be projected as a subject image.
FIGS. 5(a) and (b) are views showing the structure of another conventional CCTV camera which provides an infrared cutoff filter inside a lens tube.
The CCTV camera comprises a camera body 100B and a lens tube 200B fixed in the front thereof. Unlike the conventional example shown in FIG. 4, an infrared cutoff filter 110 and a filter-driving actuator 230 are provided inside a lens tube 200B, not inside a camera body 100B. The image pickup device 130 and the diaphragm 210 are the same as in the example shown in FIG. 4.
In addition, in this CCTV camera, a dummy filter 111 is provided adjacent to the infrared cutoff filter 110. The dummy filter 111 comprises a translucent parallel plane panel having nearly the same thickness as that of the infrared cutoff filter 110 and serves to prevent light from being incorrectly focused to the image pickup device 130 due to any difference in the length of the light path, occurring when the infrared cutoff filter 110 is placed in the light path and away from the light path, by compensating for such difference.
Consequently, the infrared cutoff filter 110 and the dummy filter 111 are installed on the same holder (not shown) so that either the infrared cutoff filter 110 or the dummy filter 111 can be placed in the light path L by driving the holder with the filter-driving actuator 230.
Since the conventional infrared cutoff filter is relatively thick (0.5 mm or more in thickness), in a CCTV camera described in Patent Document 1, a diaphragm device in which an infrared cutoff filter is provided integrally is structured while avoiding the complication of diaphragm structure by disposing the infrared cutoff filter on one surface side of a diaphragm board (not shown) when a diaphragm blade is disposed on the other surface side of the diaphragm board.
Patent Document 1: Japanese Patent Laid-open 2002-189238
In the conventional CCTV camera shown in FIG. 4, the infrared cutoff filter 110 is disposed inside the camera body 100A. However, since the camera body 100A has become smaller in recent CCTV cameras, it has become difficult to provide the infrared cutoff filter 110 and its driving mechanism (actuator 230) inside the camera body 100A itself.
Consequently, provision of the diaphragm 230 together with the infrared cutoff filter 110 in the lens tube 200B as shown in FIG. 5 becomes a promising structure. Especially, as described in Patent Document 1, installation of an infrared cutoff filter and its driving mechanism integrally on a diaphragm device has become common.
However, since a relatively thick infrared cutoff filter is used in a diaphragm device with a conventional infrared cutoff filter installed integrally as is described in Patent Document 1, the infrared cutoff filter and diaphragm blades must be disposed on the top and bottom faces of a diaphragm board respectively when considering the workability of the diaphragm blade and the infrared cutoff filter. This limits the downsizing of the diaphragm device. Further, to compensate for focusing, a dummy filter, in addition to the infrared cutoff filter, needs to be used in order to mrake the length of the light path equal. This also makes it difficult to downsize the diaphragm. Moreover, since the dummy filter is used in addition to the thick infrared cutoff filter, the weight of the filter must also be increased, which leads to a larger filter driving system. Consequently, it becomes difficult to meet the demand of reduction in size and weight of the lens tube.
Considering the above-described situation, an object of the present invention is to provide a diaphragm device which integrally provides an optical filter that can be inserted into and retracted from a light path, and is possible to reduce in size and weight so that it can be simply fixed to a lens tube of, for instance, a CCTV camera.
A diaphragm device of a first invention comprises: a diaphragm board having an aperture forming a light path; a diaphragm blade disposed on one face of the diaphragm board, and adjusting the aperture of the diaphragm for the light path by sliding along the board face; a diaphragm driving device driving the diaphragm blade to adjust the aperture of the diaphragm for the light path; an optical filter having transmission characteristics in accordance with a wave length; and a filter driving device to insert the optical filter into and retract it from the light path, wherein the above-described optical filter is formed in a thin film, disposed on one face side of the diaphragm board, and provided slidably along the diaphragm blades.
In the diaphragm device of the present invention, since the optical filter is formed in a thin film, disposed together with the diaphragm blades on one face of the diaphragm board, and provided slidably along the diaphragm blades, the structure can be simpler than that of the conventional example in which the diaphragm blades and the optical filter are disposed on both the front and bottom faces of the diaphragm board respectively. Further, since the optical filter is formed in a thin film, the optical filter can be disposed in a narrow space such as a gap between the diaphragm blades, a gap between the diaphragm blades and the diaphragm board, or the like. Furthermore, the optical filter can be incorporated smoothly without giving any trouble to the movement of the diaphragm blades so that it maintains its own sliding function.
Therefore, the diaphragm device can be downsized even though the optical filter is integral to the diaphragm device insertably into and retractably from the optical path. Further, by forming the optical filter in a thin film, a difference in the length of the light path between the time when the optical filter is in the light path and the time when it is not can be made substantially zero. Therefore, a dummy filter for preventing light from being incorrectly focused is not necessary. As a result, it becomes possible to eliminate weight increase or space increase as much as possible when the optical filter is assembled, to improve easiness in assembling of the optical filter to the lens tube or the like, and also to contribute to reduction in size and weight of the lens tube and the like.
A second invention relates to the diaphragm device according to claim 1, wherein two sheets of the above-described diaphragm blades are provided in a layer, and the optical filter formed in a thin film as described above is disposed between those two sheets of the diaphragm blades.
In the diaphragm device of the present invention, since the optical filter is disposed in a gap between two sheets of the diaphragm blades, a special space for disposing the optical filter becomes unnecessary, which enables to downsize the diaphragm device. This became possible because the optical filter was formed in a thin film.
A third invention relates to the diaphragm device according to claim 1 or claim 2, wherein the optical filter is an infrared cutoff filter blocking light in the infrared region, and formed in a thin film of 0.25 mm or less in thickness.
Since the thin film having a thickness of 0.25 mm or less is used as an optical filter in the diaphragm device of the present invention, it is possible to make the difference in the length of light path resulted from existence and non-existence of the optical filter in the light path negligibly small. Therefore, it becomes unnecessary to consider prevention of light from being incorrectly focused in optical design, and a dummy filter becomes unnecessary, which makes it possible to realize downsizing. Further, since the dummy filter is not necessary and the optical filter itself is made thin and light weighted, a driving force of the filter driving device can be made small, resulting in downsizing of the filter driving device. Since the optical filter is an infrared cutoff filter which passes through visible light region and blocks light in the infrared (near-infrared) region, it is suitable for a diaphragm device to be used for a CCTV camera. When photographing at night, light in the infrared region are allowed to pass through to take photographs by retracting the optical filter from the light path, and when photographing in the daytime, light in the infrared region is blocked by inserting the optical filter in the light path, enabling to take photographs.
A fourth invention relates to the diaphragm device according to anyone of claim 1 to claim 3, wherein the optical filter is pivotably supported by a shaft provided at one end of the diaphragm board, and is inserted into and retracted from the light path by being pivoted around the shaft.
A system to slide the optical filter along the diaphragm blade may be a linear movement type or pivot type. However, the diaphragm device of the present invention adopts a pivot type in which the diaphragm device pivots around a shaft provided at the end portion of the diaphragm board, which enables the optical filter to pivotably slide directly without being fixed to a holder or the like, so that the driving system of the optical filter can be made of a space-saving type with a simple structure. Further, by adopting a pivot type (pivotably sliding type), it becomes possible to drive the optical filter without undue stress in a small gap between the diaphragm blades.
A fifth invention relates to the diaphragm device according to anyone of claim 1 to claim 4, wherein both the diaphragm driving device and filter driving device are disposed on the same side of the light path on the diaphragm board.
In the diaphragm device of the present invention, the diaphragm driving device and the filter driving device which are relatively large parts are provided on the same sides of the light path. That is, the parts (diaphragm driving device and filter driving device) having a relatively large dimensions in thickness direction of the diaphragm board are not disposed on both sides sandwiching the light path, but are disposed on one side of the diaphragm board together, which makes the opposite side thin. Therefore, when the diaphragm device is assembled to the lens tube, the diaphragm device can be assembled to the lens tube without undue stress and neither of the driving devices serves as a drag, while inserting the thin portion of the diaphragm device first into the lens tube from the side, thus enabling to assemble the diaphragm device to the lens tube or the like with ease.
A sixth invention relates to the diaphragm device according to any one of claim 1 to claim 5, wherein the filter driving device is provided with a filter holding device holding the optical filter at a first position magnetically when the optical filter is at the first position side rather than at a middle position of the first position in the light path and a second position departing from the light path, holding the optical filter at the second position magnetically when the optical filter is at the second position side rather than at the middle position.
In this diaphragm device, excepting when the optical filter is driven to insert into and retract from the light path, the optical filter can be held securely at either the first position or the second position by magnetic force. Therefore, at the time of transmitting the inserting and retracting movements of the optical filter to the optical filter, power supply to the filter driving device can be suspended so that the power consumption of the filter driving device can be reduced.
A seventh invention relates to the diaphragm device according to claim 6, wherein the filter holding device comprises: a permanent magnet provided on a rotor of the motor driving the optical filter, and a magnetic piece disposed at a position in equal distance from mutually adjacent north and south poles of the permanent magnet, when the optical filter is driven toward the middle of the path between the first and second positions, generating force of attraction between the magnetic piece and either the north pole or the south pole, thereby causing the rotor to pivot.
In this diaphragm device, when power supply to the motor which drives the optical filter is suspended, the optical filter is automatically positioned at either the first position or the second position by force of attraction generated between the permanent magnet and the magnetic piece according to the rotor position at the time. That is, when power supply to the motor is suspended in a state that the optical filter is moved to the first position side from the middle position, the optical filter is moved to the first position and securely held by magnetic power acting between the permanent magnet and the magnetic piece, and when power supply to the motor is suspended in a state that the optical filter is moved to the second position side from the middle position, the optical filter is moved to the second position and held by magnetic power acting between the permanent magnet and the magnetic piece. Since this state is maintained as it is due to suspension of the power supply to the motor, unnecessary power consumption of the motor can be cut so that the life of the battery can be prolonged.
An eighth invention relates to the diaphragm device according to any one of claim 1 to claim 7, wherein an ND filter different from the optical filter is provided in a transmitting hole forming a diaphragm aperture of the diaphragm blades, and the ND filter has spectroscopic transmittance characteristics in which the transmittance in the infrared region is substantially equal to that in the visible light region.
The diaphragm device of the present invention can reduce the transmission amount of the infrared light to the same transmission amount of light in the visible region by the ND filter when photographing at night using, for instance, a CCTV camera. Accordingly, the infrared light can be prevented from excessively exposed.
That is, assuming that the diaphragm device is installed on a CCTV camera, in this type of the conventional diaphragm device, the ND filter is generally affixed on the diaphragm blade at the position above the diaphragm aperture in order to widen a control range of the light amount on photographing in monochrome at night when no infrared cutoff filter is inserted. However, an ordinary ND filter is apt to take a state that the transmittance of the infrared light is increased, that is, a state that the infrared light passes through. Therefore, the infrared light at the time of photographing in monochrome can not be controlled uniformly in a similar manner to the visible light, the transmitting amount of infrared light becomes larger than that of the visible light, which makes a portion of a subject strongly lighted by the infrared light bright so that the photographed image is hard to see. As for this point, the diaphragm device of the eighth invention realizes reduction of transmission amount of the infrared light to the same degree as light amount in the visible light region by ND filter. Accordingly, a portion of a subject strongly lighted by infrared light does not become too bright, so that a photographed image being easy to see can be obtained.